GIT – A Redundant Array of Independent Drives (or ), also known as Redundant Array of Inexpensive Drives (or ) () is an term for data storage schemes that divide and/or replicate data among multiple hard drives.

RAID can be designed to provide increased data reliability or increased I/O performance, though one goal may compromise the other. There are 10 RAID level. But which one is recommended for data safety and performance considering that hard drives are commodity priced?

I did some research in last few months and based upon my experince I started to use RAID10 for both Vmware / XEN Virtualization and database servers. A few MS-Exchange and Oracle admins also recommended RAID 10 for both safety and performance over RAID 5.

Quick RAID 10 overview (raid 10 explained)

RAID 10 = Combining features of RAID 0 + RAID 1. It provides optimization for fault tolerance.

RAID 0 helps to increase performance by striping volume data across multiple disk drives.

RAID 1 provides disk mirroring which duplicates your data.

In some cases, RAID 10 offers faster data reads and writes than RAID 5 because it does not need to manage parity.

Fig.01: Raid 10 in action

RAID 5 vs RAID 10

From Art S. Kagel research findings:

If a drive costs $1000US (and most are far less expensive than that) then switching from a 4 pair RAID10 array to a 5 drive RAID5 array will save 3 drives or $3000US. What is the cost of overtime, wear and tear on the technicians, DBAs, managers, and customers of even a recovery scare? What is the cost of reduced performance and possibly reduced customer satisfaction? Finally what is the cost of lost business if data is unrecoverable? I maintain that the drives are FAR cheaper! Hence my mantra:
NO RAID5! NO RAID5! NO RAID5! NO RAID5! NO RAID5! NO RAID5! NO RAID5!

Is RAID 5 Really a Bargain?

Cary Millsap, manager of Hotsos LLC and the editor of Hotsos Journal found the following facts – Is RAID 5 Really a Bargain?“:

  • RAID 5 costs more for write-intensive applications than RAID 1.
  • RAID 5 is less outage resilient than RAID 1.
  • RAID 5 suffers massive performance degradation during partial outage.
  • RAID 5 is less architecturally flexible than RAID 1.
  • Correcting RAID 5 performance problems can be very expensive.

My practical experience with RAID arrays configuration

To make picture clear, I’m putting RAID 10 vs RAID 5 configuration for high-load database, Vmware / Xen servers, mail servers, MS – Exchange mail server etc:

RAID Level Total array capacity Fault tolerance Read speed Write speed
RAID-10
500GB x 4 disks
1000 GB 1 disk 4X 2X
RAID-5
500GB x 3 disks
1000 GB 1 disk 2X Speed of a RAID 5 depends upon the controller implementation

You can clearly see RAID 10 outperforms RAID 5 at fraction of cost in terms of read and write operations.

A note about backup

Any RAID level will not protect you from multiple disk failures. While one disk is off line for any reason, your disk array is not fully redundant. Therefore, old good tape backups are always recommended.

What are the different RAID levels for / UNIX and Windows Server?

What are the different RAID levels? Which one is recommended for file server and database server?

A. A Redundant Array of Independent Drives (or Disks), also known as Redundant Array of Inexpensive Drives (or Disks) (RAID) is an term for data storage schemes that divide and/or replicate data among multiple hard drives. RAID can be designed to provide increased data reliability or increased I/O performance, though one goal may compromise the other.

There are total 10 types of RAID levels:

  • RAID level 0
  • RAID level RAID level 1
  • RAID level 2
  • RAID level 3
  • RAID level 4
  • RAID level 5
  • RAID level 6
  • RAID level 10
  • RAID level 50
  • RAID level 0+1

Commonly used RAID levels for UNIX / Linux and Windows server

Following are commonly used RAID levels :

RAID level Minimum hard disks Suggested application Notes
RAID 0 – Striped Set without parity 2 Hard disks 1. Video Production and Editing
2. Image Editing
3. Any application requiring high bandwidth
Provides improved performance and additional storage but no fault tolerance from disk errors or disk failure. Any disk failure destroys the array, which becomes more likely with more disks in the array.
RAID 1 –MirroredSet (2 disks minimum) without parity. 2 Hard disks 1. Office application
2. Financial application
3. Payroll application etc
Provides fault tolerance from disk errors and single disk failure. Increased read performance occurs when using a multi-threaded operating system that supports split seeks, very small performance reduction when writing. Array continues to operate so long as at least one drive is functioning
RAID 5 3 Hard disks 1. File and Application servers
2. Internet Web, E-mail servers
3. Intranet servers
Highest Read data transaction rate, Medium Write data transaction rate, Overall good (aggregate) transfer rate. drive failure requires replacement, but the array is not destroyed by a single drive failure. Upon drive failure, any subsequent reads can be calculated from the distributed parity such that the drive failure is masked from the end user. The array will have data loss in the event of a second drive failure and is vulnerable until the data that was on the failed drive is rebuilt onto a replacement drive
RAID 10 (nested RAID 1+0) 4 Hard disks 1. Database server (such as Oracle / MySQL / MS-SQL) which requiring high performance and fault tolerance Provides fault tolerance and improved performance but increases complexity.

Thảo luận bài viết tại forum : http://forum.gocit.vn/threads/raid-5-vs-raid-10-recommended-raid-for-safety-and-performance.463/

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